1. Field of the Invention
The present invention relates to an effect circuit that gives effect such as distortion to a music signal that is input from an electric musical instrument such as an electric guitar or an electric bass, an electronic musical instrument such as a keyboard, or a toy.
2. Description of the Related Art
In playing an electric musical instrument such as an electric guitar or an electric bass, an electronic musical instrument such as a keyboard, or a toy, an effect circuit that gives effect such as distortion to a music signal that is input from the electric musical instrument, the electronic musical instrument, or the like is used. As the effect circuit, a distortion circuit that gives distortion effect to the music signal by clipping the music signal symmetrically, an over drive circuit that gives the distortion effect to the music signal by clipping the music signal asymmetrically and so on are known (For example, see international publication No. WO2003/077232).
FIG. 9 is a diagram illustrating a circuit configuration of a conventional effect circuit that gives the distortion effect to the music signal by clipping the music signal symmetrically. As illustrating in FIG. 9, an effect circuit 100 includes an operational amplifier U1, zener diodes D1 and D2, resistors R1 to R3, condensers C1 to C4, and a variable resistor VR1. The operational amplifier U1 amplifies the music signal that is input from the electric musical instrument. The music signal is input to a positive input terminal of the operational amplifier U1. Bias voltage Vcc/2 is given to the positive input terminal of the operational amplifier U1 via the resistor R1. The music signal that is output from an output terminal is returned to a negative input terminal of the operational amplifier U1. The variable resistor VR1 is a feedback resistor that is provided between the negative input terminal of the operational amplifier U1 and the output terminal of the operational amplifier U1, namely, in feedback part of the operational amplifier U1. The resistor R2 is an input resistor that is connected to the negative input terminal of the operational amplifier U1. Amplification factor of the operational amplifier U1 is decided by the resistor R2 and the variable resistor VR1. Namely, the operational amplifier U1 amplifies the music signal with the amplification factor that is decided by the resistor R2 and the variable resistor VR1. For example, a user can change a resistance value of the variable resistor VR1 by operating an operation knob, not shown, that is provided at an enclosure of the effect circuit 100.
The zener diodes D1 and D2 clip the music signal so as to give the distortion effect to the music signal. Each of cathodes of the zener diodes D1 and D2 is connected, and the zener diodes D1 and D2 are provided in parallel with the variable resistor VR1. Namely, the zener diodes D1 and D2 are provided in the feedback part of the operational amplifier U1.
The resistor R3 is provided in parallel with the output terminal of the operational amplifier U1 and is earthed at one end. The condensers C1 to C4 are provided at positions that are illustrated.
In the effect circuit 100, a positive side music signal is clipped by zener voltage of the zener diode D1. A negative side music signal is clipped by zener voltage of the zener diode D2. FIG. 10 is a graph illustrating the music signal that the conventional effect circuit 100 outputs. A vertical axis illustrates voltage [v] and a horizontal axis illustrates time [ms].
FIG. 11 is a diagram illustrating a circuit configuration of another conventional effect circuit. The other conventional circuit 100 illustrated in FIG. 11 is compared with the conventional circuit 100 illustrated in FIG. 9 and a configuration that the zener diodes D1 and D2 are provided in parallel with the output terminal of the operational amplifier U1 is mainly different. Further, a resister R4 and a condenser C5 are added to the other conventional effect circuit 100 illustrated in FIG. 11 compared to the conventional effect circuit 100 illustrated in FIG. 9. In the effect circuit 100 illustrated in FIG. 11, the positive side music signal that is output from the operational amplifier U1 is clipped by the zener voltage of the zener diode D1. The negative side music signal that is output from the operational amplifier U1 is clipped by the zener voltage of the zener diode D2.
A zener diode has characteristics that current flows suddenly when voltage of opposite direction becomes bigger than the zener voltage. Thus, when the music signal is clipped by the zener diode, as illustrating in FIG. 10, waveform is clipped steeply and an odd-harmonic component is emphasized. Therefore, the music signal that is output from the conventional effect circuit is rough sound as the distortion.